What's a Two-Step Rev Limiter, And How Does it Help in Drag Racing?

If you've watched any form of drag racing where turbochargers are involved, you've heard talk of two different types of engine equipment: two-step rev limiters, and anti-lag. Both are responsible for some massive exhaust flames erupting from a car that's revving at the starting line. But what's the difference between the two? How do they work? And what do they do to help your racing launch and drag strip ET?

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As always, Jason Fenske of YouTube's Engineering Explained is here to demystify the technology that helps racers win. With his trusty whiteboard illustrations, Fenske helps us understand the difference between a two-step rev limiter, anti-lag, and the launch control systems that some manufacturers now include from the factory on their high-performance cars.

Basically, it all boils down to ignition control. An aftermarket two-step rev limiter lets you set one (lower) limiter for launch, and a higher limit for when you're upshifting as you accelerate away. Anti-lag does something similar, but it's focused on dumping fuel into the exhaust system, so it can ignite further downstream from the combustion chamber and help the turbo or turbos spool up to build boost.

Fenske also put together a video demonstrating the anti-lag process on the new Veloster N, which comes standard with the feature from the factory. The process is similar, using timing to retard ignition and push a hot air-fuel mixture into the exhaust to keep the turbo spooled off-throttle. Hyundai says its main purpose is for sound, but in the car's most aggressive drive mode, it does actually work like a real anti-lag system. Clever stuff.

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